1. Field of the Invention
The present invention relates to a pressurized-fluid cartridge useful for a variety of domestic purposes, such as for discharging draft beer from a beer dispenser or expelling soda water from a soda siphon. More particularly, the present invention is concerned with a safety closure used to close the mouth of such high-pressure container.
2. Description of the Prior Art
It has been known that, when the pressure in such a cartridge or high-pressure container is raised to an unduly high level by the increase in the ambient temperature caused as in an occasion where the cartridge, which has not yet been used, is inadvertently put into a fire, the closure having a wall thickness smaller than that of the container portion of the cartridge is outwardly bowed until the closure everts and explodes, so that the gas under pressure is jetted through the ruptured opening in the closure to propell and leap the cartridge at a dangerously high velocity and in an uncertain direction.
In an attempt to eliminate such dangerous conditions, it has been proposed in U.S. Pat. No. 3,038,627 to provide a thin-walled area or zone at a localized portion of a pressure container so that, when the pressure within the container is raised to an unduly high level, a small hole is formed in the thin-walled zone of the container to permit the pressure to be relieved through the small hole at a low rate for thereby preventing the container from otherwise being strongly propelled to leap at a dangerously high velocity. It has also been proposed in U.S. Pat. No. 4,219,126 to provide a thin-walled portion in a closure sealed to the mouth of a high-pressure gas container.
The prior art high-pressure gas containers, including those disclosed in the U.S. patents referred to above, are usually made from mild steel from the view points of workability and cost of manufacture. Although the containers are plated or coated with paint so as to guard the containers against corrosion, the localized thin-walled portions provided in the containers or in the closures are attacked by water contained either in the pressurized gases in the containers or in the atmospheric air. Thus, the thin-walled portions tend to be corroded in a long time until pin holes are formed to permit gaseous pressures to escape therethrough during storage of the containers or cartridges.
Particularly, the gas cartridge disclosed and claimed in U.S. Pat. No. 4,219,126 is provided with a conical recess formed in the central section of the closure of the container. The design of the recess calls for very strict dimensional relationship between the area of the opening of the recess in the closure and the wall thickness of the recessed or thinned section of the closure. It has been known from experimental tests that the wall thickness of the thinnest part of the closure, i.e., the wall thickness at the bottom of the conical recess in the closure, must be not greater than 0.08 mm in order to assure that the closure can surely act as a safety closure. If the wall thickness is greater than 0.08 mm, there occurs a very dangerous possibility that the closure is bursted widely beyond the recessed section of the closure toward the outer peripheral edge thereof. In order to avoid such a dangerous possibility, therefore, the wall thickness of the thinnest point of the recessed section of the closure must normally be about 0.05 mm.
However, very minute technique and skill are required to provide the cartridge closures with recesses which satisfy the above-discussed dimensional requirement. In addition, it is impossible to visibly judge if recessed cartridge closures so made would surely satisfy the requirement for safety closures.
In addition, because the prior art cartridge closures are usually made of a metal, such as mild steel, so that the closures can be welded to the cartridge bodies or containers which are made from mild steel, as pointed out previously, it will be appreciated that the closures are easily corroded by the water contained in the pressurized gases in the cartridges or in the atmospheric air. Thus, pin holes are formed by corrosion in the thin-walled points of the bottoms of the recesses in the cartridge closures in comparatively short time from the manufacture of the cartridges, so that gaseous contents of the cartridges all escape therefrom during storage of the cartridges. Moreover, because the closures of the prior art gas cartridges are each formed by a single layer of metal, the closure metal layer will widely evert and explode from the thinnest point of the metal layer to form a wide opening when the gaseous pressure in the cartridge is raised to an unduly high level. Thus, the gas at the high pressure rushes out of the exploded cartridge through the exploded opening in the closure to propell and leap the cartridge at a very dangerously high velocity.